An investigation of the atmospheres of O-type main sequence stars by non-LTE.

Calculations of equivalent widths of N III multiplets λ4640 Å, λ4097 Å, λ4379 Å have been performed on the basis of a detailed solution of the coupled statistical-equilibrium and radiative-transfer equations for a multiline, multilevel, multi-ion ensemble and for non-LTE model atmospheres with T_eff = 32500 - 55000K and lg g = 3.3, 3.5, 4.0, 4.5. The comparison of the observed equivalent widths with the calculated ones by non-LTE of H, He I, He II, C III, C IV, N III, N IV lines in the visual spectra of O-type stars permitted to establish that the model atmospheres with T_eff and lg g determined from H and He lines satisfactorily predict also the behaviour of absorption and emission lines of light ions for 8 stars from the 10 investigated ones. The normal abundances of carbon and nitrogen have been used and the microturbulent velocity ξ_t was found to be 0 - 5 km/s.